The present invention relates generally to infrared scanning systems and more specifically to infrared target acquisitions systems for detecting heat producing bodies.
Surveillance systems have been of prime importance to the Navy in both detecting and recognizing enemy and friendly ships and aircraft. Numerous methods and devices have been developed to accomplish these ends. For example, complex monopulse radar systems have been developed that operate at X-band frequencies which can distinguish minute detail of targets at great distances. However, these systems often require expensive computer processing equipment to process the high frequency signals for display. In addition, the monopulse hardware is extremely complex and expensive.
Infrared scanning systems have also been used to detect targets. Basically two types have been known to the prior art. One type uses a linear array of detectors located along the elevation axis which are electronically scanned as they are mechanically rotated in the azimuthal plane. This electronically scanned data is then fed to a television monitor at a remote location for viewing in real time. The great advantage of the infrared scanners over radar apparatus giving similar results is that they are relatively inexpensive in comparison, while still giving detailed target information in nonvisible conditions, e.g., night, fog, etc., at moderate distances. The other type uses a linear array of detectors connected to light emitting diodes (LED's) which are subsequently scanned by a television camera which transmits the picture to a television monitor at a remote location. These systems however, show only a narrow sector of the azimuthal plane at any given instant of time. It is desirable to display the entire 360.degree. azimuthal plane at once so that the viewer can search a much larger volume of space. To display the entire azimuthal plane simultaneously, a system with a much larger signal bandwidth is necessary to be compatible with the flicker fusion rate of the human eye, the bandwidth of the prior art infrared systems would allow scanning rates of only about one per second where the flicker fusion rate requires at least 30 scans per second. Although it is possible to trick the eye through different techniques, i.e., flashing a non-refreshed frame twice before presenting a second frame, placing large amounts of memory into the display, etc., rotating of the scanning head at large angular rates has been explored instead.
One of the problem areas in driving a system at large angular rates is how to pick off the signals from each detector in the array. Normally a mechanically rotating system uses slip rings to accomplish this objective. However the use of a large number of slip rings, one for each channel, in a rapidly rotating system would introduce noise and mechanical problems that are best avoided.
Additionally, the use of slip rings resigns the designer to rotating not only the optics but all the electronic preamp circuits and the detector/cooler assembly at these high rates. It was decided therefore to seek another solution.
Another problem arising out of such a system is how to display, in real time, all the information gathered. A cursory examination of the bandwidth requirements will show, that the display must be capable of handling several hundred megahertz. Bandwidth considerations alone rule out the use of a conventional CRT display. A multigun CRT was considered. However even a ten gun CRT is inadequate to handle the required bandwidth.